Areva - The Fukushima Daiichi Incident

8/2/2019 Areva - The Fukushima Daiichi Incident

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Impatto Ambientale e bilancio CO2

http://energyfromthorium.com/2011/03/30/areva-fd-presentation/


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The

Fukushima DaiichiIncident

1. Plant Design2. Accident Progression

3. Radiological releases

4. Spent fuel pools

5. Sources of Information

Matthias Braun

PEPA4-G, AREVANP GmbH

[email protected]


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The Fukushima Daiichi Incident1. Plant Design

Fukushima Daiichi (Plant I)

Unit I - GE Mark I BWR (439 MW), Operating since 1971

Unit II-IV - GE Mark I BWR (760 MW), Operating since 1974


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Service Floor


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Piano di servizio del reattore

(Acciaio)

Costruzione in cemento armatodi protezione reattore

Nocciolo del reattore

Camera reattore in pressione

Contenimento (parete asciutta)

Contenimento (parete umida) /Camera condensazione (toro)

Spend Fuel Pool

Linea ritorno vapore

Alimentazione Acqua


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The Fukushima Daiichi Incident2. Accident progression

11.3.2011 14:46 - Earthquake

Magnitude 9

Power grid in northern Japan fails

Reactors itself are mainlyundamaged

SCRAM

Power generation due to Fissionof Uranium stops

Heat generation due to radioactive

Decay of Fission Products After Scram ~6%

After 1 Day ~1%

After 5 Days ~0.5%

Safety Control Rod Automatic Motion


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Containment Isolation

Closing of all non-safety relatedPenetrations of the containment

Cuts off Machine hall

If containment isolation succeeds,a large early release of fissionproducts is highly unlikely

Diesel generators start

Emergency Core cooling systemsare supplied

Plant is in a stable save state


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11.3. 15:41 Tsunami hits the plant

Plant Design for Tsunami height ofup to 6.5m

Actual Tsunami height >7m

Flooding of

Diesel Generators and/or

Essential service water buildingcooling the generators

Station Blackout

Common cause failure of thepower supply

Only Batteries are still available

Failure of all but one Emergencycore cooling systems


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Reactor Core Isolation Pump still

available Steam from the Reactor drives a

Turbine

Steam gets condensed in theWet-Well

Turbine drives a Pump

Water from the Wet-Well getspumped in Reactor

Necessary:

Battery power

Temperature in the wet-wellmust be below 100C

As there is no heat removal fromthe building, the Core isolationpump cant work infinitely


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Reactor Isolation pump stops

11.3. 16:36 in Unit 1(Batteries empty)

14.3. 13:25 in Unit 2(Pump failure)


Decay Heat produces still steam inReactor pressure Vessel

Pressure rising

Opening the steam relieve valves Discharge Steam into the Wet-Well

Descending of the Liquid Level inthe Reactor pressure vessel


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Pressure rising




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Pressure rising




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Pressure rising




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Pressure rising




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Measured, and here referenced

Liquid level is the collapsed level.The actual liquid level lies higherdue to the steam bubbles in theliquid

~50% of the core exposed

Cladding temperatures rise, but stillno significant core damage

~2/3 of the core exposed

Cladding temperatureexceeds ~900C

Balooning / Breaking of thecladding

Release of fission products formthe fuel rod gaps


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~3/4 of the core exposed

Cladding exceeds ~1200C

Zirconium in the cladding starts toburn under Steam atmosphere

Zr + 2H20 ->ZrO2 + 2H2

Exothermal reaction furtherheats the core

Generation of hydrogen

Unit 1: 300-600kg

Unit 2/3: 300-1000kg

Hydrogen gets pushed via the

wet-well, the wet-well vacuumbreakers into the dry-well


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at ~1800C [Unit 1,2,3]

Melting of the Cladding

Melting of the steel structures

at ~2500C [Block 1,2]

Breaking of the fuel rods

debris bed inside the core

at ~2700C [Block 1]

Melting of Uranium-Zirconiumeutectics

Restoration of the water supplystops accident in all 3 Units

Unit 1: 12.3. 20:20 (27h w.o. water)

Unit 2: 14.3. 20:33 (7h w.o. water)

Unit 3: 13.3. 9:38 (7h w.o. water)


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Release of fission products duringmelt down

Xenon, Cesium, Iodine,

Uranium/Plutonium remain in core

Fission products condensate toairborne Aerosols

Discharge through valves into waterof the condensation chamber

Pool scrubbing binds a fraction ofAerosols in the water

Xenon and remaining aerosolsenter the Dry-Well

Deposition of aerosols on surfacesfurther decontaminates air


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Containment

Last barrier between Fission

Products and Environment Wall thickness ~3cm

Design Pressure 4-5 bar

Actual pressure up to 8 bars

Normal inert gas filling - Nitrogen Hydrogen from core oxidation

Boiling condensation chamber(like a pressure cooker)

Depressurization of the

containment

Unit 1: 12.3. 4:00

Unit 2: 13.3 00:00

Unit 3: 13.3. 8.41


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Positive and negative Aspects ofdepressurizing the containment

Removes Energy from the Reactorbuilding (only way left)

Reducing the pressure to ~4 bar

Release of small amounts of

Aerosols (Iodine, Cesium ~0.1%)

Release of all noble gases

Release of Hydrogen

Gas is released into the reactor

service floor Hydrogen is flammable


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Unit 1 und 3

Hydrogen burn inside the reactorservice floor

Destruction of the steel-frame roof

Reinforced concrete reactorbuilding seems undamaged

Spectacular but minor safetyrelevant


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Unit 2

Hydrogen burn inside the reactorbuilding

Probably damage to thecondensation chamber(highly contaminated water)

Uncontrolled release of gas from

the containment Release of fission products

Temporal evacuation of the plant

High local dose rates on the plantsite due to wreckage hinder furtherrecovery work

No clear information's why Unit 2behaved differently


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Current status of the Reactors

Core Damage in Unit 1,2, 3 Building damage due to various

burns Unit 1-4

Reactor pressure vesselsflooded in all Units with mobilepumps

At least containment in Unit 1flooded

Further cooling of the Reactorsby releasing steam to theatmosphere

Only small further releases offission products can be expected


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The Fukushima Daiichi Incident3. Radiological releases

Directly on the plant site

Before Explosion in Unit Block 2

Below 2mSv / h

Mainly due to released radioactive noble gases

Measuring posts on west side. Maybe too small values measured due to wind

After Explosion in Unit 2 (Damage of the Containment)

Temporal peak values 12mSv / h

(Origin not entirely clear)

Local peak values on site up to 400mSv /h (wreckage / fragments?)

Currently stable dose on site at 5mSv /h

Inside the buildings a lot more

Limiting time of exposure of the workers necessary


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Outside the Plant site

As reactor building mostly intact=> reduced release of Aerosols (not Chernobyl-like)

Fission product release in steam=> fast Aerosol grows, large fraction falls down in the proximity of the plant

Main contribution to the radioactive dose outside plant are the radioactive

noble gases Carried / distributed by the wind, decreasing dose with time

No Fall-out of the noble gases, so no local high contamination of soil

~20km around the plant

Evacuations were adequate Measured dose up to 0.3mSv/h for short times

Maybe destruction of crops / dairy products this year

Probably no permanent evacuation of land necessary


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GRS.de

~50km around the plant

Control of Crop / Dairy products

Usage of Iodine pills(Caution, pills can interferewith heart medicine)


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The Fukushima Daiichi Incident4. Spend fuel pools

Spend fuel stored in Pool on

Reactor service floor Due to maintenance in Unit 4 entire

core stored in Fuel pool

Dry-out of the pools

Unit 4: in 10 days

Unit 1-3,5,6 in few weeks

Leakage of the pools due toEarthquake?

Consequences

Core melt on fresh air

Nearly no retention of fissionproducts

Large release


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Unit 4: in 10 days



Consequences



Large release


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Unit 4: in 10 days



Consequences



Large release

It is currently unclear if releasefrom fuel pool already happened

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Areva - The Fukushima Daiichi Incident